You are prompted to give passphrases for each key found by the SOCKS Proxy in turn.

After the passphrase has been given, it will be stored in cache and the key
can be used non-interactively.

Note: The passphrase cache is used only for transparent tunneling
with ssh-socks-proxy. Use ssh-add2 and ssh-agent2
to cache passphrases for ssh2, scp2, and sftp2.
See the ssh-add2 and ssh-agent2 man pages for more
information (Appendices ssh-add2 and ssh-agent2).